1. Field of the Invention
The present invention relates to a laminate with improved copper-resin adhesion that is useful for manufacturing a laminate of copper/copper alloy (hereinafter, noted simply as copper) and resin, i.e., a printed circuit board, and a method of manufacturing the laminate.
2. Description of the Related Art
A multilayered printed circuit board has a laminate having a plurality of electroconductive layers with insulating layers interposed therebetween. Through-holes for electrical connection of the respective electroconductive layers are formed on the multilayered printed circuit board, and the multilayered printed circuit board has an inner surface plated with copper. Alternatively, the through-holes are filled with an electroconductive paste.
The conductive layers comprise copper while the insulating layer comprises resin, which have poor adhesion to each other. For improving the adhesion of copper to resin, in general, a copper surface is blackened, i.e., treated with a high-temperature strong-alkali aqueous solution so as to form a fine acicular copper oxide thereon. The method is called a black oxide technique.
However, the acicular copper oxide formed on the copper surface will be dissolved easily in an acidic plating solution during a step of plating the through-holes. The phenomenon in which the copper oxide is dissolved is called haloing. A method applied for avoiding this problem is reduction of the acicular copper oxide into copper with a reducer while keeping its shape, so that the copper oxide becomes difficult to dissolve in an acidic plating solution. However, this method is not desirable since it increases the steps in the process of an already inherently-inefficient blackening treatment that takes much time.
Another production method with fewer steps for improving adhesion of the copper surface to resin is roughening the copper surface with a microetchant.
For example, JP 2923524 describes roughening a copper surface by using an aqueous solution containing a cupric ion, an organic acid having an acid dissociation constant (pKa) of not more than 5, and a halogenous ion. However, simple roughening of a copper surface cannot always provide sufficient adhesion to resin.
JP 2740768 describes the use of an aqueous solution containing an inorganic acid, an oxidizer, a corrosion inhibitor such as azole and also a surfactant, for etching and roughening the copper surface and at the same time, for forming an azole complex on the copper surface.
However, since the oxidizer will be decomposed easily, etching and formation of the azole complex tend to be unstable, resulting in insufficient adhesion to resin.
Any of U.S. Pat. No. 36,455,772, JP-A-61(1986)-266241, and JP-A-11(1999)-43778 describes a method of forming a coating film on a copper surface by adsorbing an azole compound in the surface, thereby improving its adhesion to resin.
However, since the aqueous solution of the azole compound contains no organic acids, the coating film of the azole compound formed on the copper surface is thin and insufficient in adhesion to resin.
JP-A-6(1994)-287774 describes a copper microetchant containing an azole compound, a cupric ion source, an organic acid and a complexing agent. JP-A-7(1995)-292483 describes a copper microetchant containing an azole compound, a cupric ion source, an organic acid and a halogenous ion.
Since each of these solutions containing azole compounds and organic acids is used for etching copper using oxidizability provided by the cupric acid complex of the azole compound, it cannot form a thick film of an azole compound on the copper surface.
JP 2923596 describes a copper anti-tarnish, which comprises an aqueous solution containing an imidazole compound, an organic acid, and a copper compound. However, the invention does not refer to adhesion between a copper plate and resin.
As described above, various methods to replace blackening in manufacturing a multilayered printed circuit board have been studied to improve the adhesion of the copper surface to resin, while satisfactory methods have not been developed yet.
For solving the above-mentioned problems, the present invention provides a laminate with improved adhesion between a surface of copper/copper alloy and a resin in a multilayered printed circuit board, and a method of manufacturing the laminate.
For achieving this object, a laminate according to the present invention is formed by adhering at least one layer of a metal selected from copper and a copper alloy to a resin layer, wherein an azole-copper complex compound coating film is formed by a contact between the surface and an aqueous solution containing an azole compound in a range from 0.1 mass % to 15 mass % and an organic acid in a range from 1 mass % to 80 mass %, and the metal layer and the resin layer are adhered to each other via the coating film of the azole-copper complex compound.
A method of manufacturing a laminate according to the present invention is used for manufacturing a laminate by adhering at least one metal layer selected from copper and a copper alloy to a resin layer, including formation of a coating film of an azole-copper complex compound by contacting the surface of the metal layer with an aqueous solution containing an azole compound in a range from 0.1 mass % to 15 mass % and an organic acid in a range from 1 mass % to 80 mass %, and adhering the metal layer and the resin layer via the coating film of the azole-copper complex compound.
A solution for forming an azole-copper complex compound according to the present invention comprises an aqueous solution containing an azole compound in a range from 0.1 mass % to 15 mass % and an organic acid in a range from 1 mass % to 80 mass %.